This study seeks to establish the relevance of middle school students' naive beliefs about knowledge and learning in science to their achievement motivation in this domain. A predominantly Hispanic and lower-income sample of 459 middle school students (sixth through eighth grades) completed measures of epistemic beliefs along with several measures of motivation. Results indicated that a belief that scientific knowledge develops and that justification is necessary to valid knowledge in science were positively related to mastery goals, task value, and self-efficacy. Epistemic beliefs were also found to predict science grades over and above the contributions of motivational factors. Surprisingly, an uncritical acceptance of authority figures and a belief in scientific knowledge as certain were more typical of students who adopted motivational states (e.g., mastery goals) previously found to be supportive of learning. The latter findings may be unique to early adolescence within the ethnic and socioeconomic status parameters of the present sample. (Contains 4 tables and 1 figure.)